Nanoscience and Nanotechnology for Chemical and Biological Defense

Downloaded by 198.27.88.209 on May 6, 2018 | https://pubs.acs.org Publication Date: December 24, 2009 | doi: 10.1021/bk-2009-1016.ch001

Chapter 1

Challenges for Chemical and Biological Protection Charles A. Bass, Jr. Defense Threat Reduction Agency, Fort Belvoir, VA 22060

The Joint Science and Technology Office for Chemical and Biological Defense (JSTO-CBD), which is operated within the Defense Threat Reduction Agency's (DTRA) Chemical and Biological Technologies Directorate, has the responsibility to develop and manage the technology base for chemical and biological passive defense capabilities. The challenge of novel protective systems focus on factors such as burden, costs, duration of performance and effectiveness against a full range of agents. These challenges require the development of materials and systems that capture, block or destroy agents more effectively than the current systems. These technology solutions must also decrease material weight and costs, while reducing burden and lessening the impact on mission performance. Specific challenges in different technology areas and some approaches to addressing them are briefly described.

Introduction The fall of the Berlin Wall two decades ago signaled the close of the Cold War and yet the approach to current capabilities for individual and collective chemical and biological protection has not sufficiently considered the evolution of the threat. Like Improvised Explosive Devices (IEDs) currently used against U.S. forces in Iraq and Afghanistan, an innovative threat force will be able to U.S. government work. Published 2009 American Chemical Society Nagarajan et al.; Nanoscience and Nanotechnology for Chemical and Biological Defense ACS Symposium Series; American Chemical Society: Washington, DC, 2009.

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4 compensate for inadequacies and synthesize new ways to deliver Chemical and Biological (CB) agents on target. So, future use of CB weapons may be characterized as immediate, intense, and local, rather than the massive barrages and tons per hectare scenarios characteristic of cold war threat analysis. Threats may include classical CB agents, as well as non-traditional agents and emerging biological threats. It also can include Toxic Industrial Chemicals/Toxic Industrial Materials (TIC/TIM) that could threaten operational forces through accidental or malicious release. As a consequence, the risk may be rising. Although, protective equipment may not have to defend against the same quantities previously established as the standard, it may have to address a broader spectrum of agents. Further, the nature of the threat may require greater availability of protection that is built-in, rather than applied on the top of vehicles, vessels, platforms, structures and standard battledress. Protection that is always present will be available when needed. Providing this continuous, built-in protection without increasing the burden on the warfighter is where the challenge lies. Meeting this challenge is the focus of science and technology efforts within the protection capability area.

Challenges Factors such as burden, costs, duration of performance, and effectiveness against the full spectrum of potential agents must be addressed. These operational challenges require the development of new materials and systems that capture, block or destroy agents more effectively than the current systems. Technology solutions must also decrease material weight and costs, while reducing burden and lessening the impact on mission performance. Specific challenges in material science can be subdivided into the technology theme areas of air purification and protective barriers. Removal of hazardous high-volatility, low-molecular weight chemical vapors is the limiting performance characteristic of adsorption-based air purification technologies. The primary challenge is to develop broad spectrum treatments, while reducing size, flow resistance, and power demand. Particulates and aerosols have increasingly become important considerations for both biological and chemical threats, but current High Efficiency Particulate Air (HEPA) technologies create significant pressure barriers (pressure drops) to airflow and have diminished performance for the smallest particles. These traditional approaches also place a significant logistical burden that limits the wide-spread application to building protection. New technologies must address the high costs as well as limited shelf and service life of filters. The development of protective barrier materials used for protective clothing addresses the spectrum of percutaneous threats, but must achieve protection with a relatively thin material over a large area. The balance of maximizing protective performance while minimizing thermal burden has been the essence of the challenge for years, and the increasing need to protect against particulates further complicates the issue. The goal of incorporating these materials into fulltime wear uniforms is especially challenging because increased durability is needed to meet service life and the threshold of acceptable thermal burden is

Nagarajan et al.; Nanoscience and Nanotechnology for Chemical and Biological Defense ACS Symposium Series; American Chemical Society: Washington, DC, 2009.


5 much lower. Self-detoxifying materials are seen as a means of increasing service-life and performance, while simultaneously decreasing thermal burden, but these materials need to be safe, shelf-stable and effective. Novel, high-performance materials often cost more, so a better understanding of human performance and the relative system science will facilitate the analysis of trade-offs to apply these materials to the greatest effect. The burden and degradation of mission performance are warfighters’ primary issues with currently fielded individual protection systems. Burden and mission degradation are based on a multitude of both cognitive and physiological factors. Some factors, such as heat burden, are well quantified, but others, such as cognitive effects of encapsulation, are not. Currently fielded and developmental individual and collective protection still use a variation of a basic design derived many decades ago. Whole system analysis is needed to determine the value of new and emerging technologies that may allow a revolutionary systems approach to individual and collective protection.

Approaches Present investments have focused on the development of the materials that will feed into a complete integrated protective ensemble. Traditionally, protective mask and protective clothing have been developed as separate programs and little has been done to co-develop CB protection with ballistic protection and on-board optical and communication sub-systems that are now part of a modern fighting ensemble. A holistic approach can balance various elements, such as power demand, mission interface and thermal burden. As a concept refinement strategy, thermal performance can be managed as an independent variable by setting the desired thermal load equal to that of a standard battledress uniform, then determine the best achievable chemical/ biological performance under that constraint. Such an approach does a better job at spurring technological innovation and will provide the user with a better understanding of the tradeoffs between performance and physiological burden. Much of the cognitive burden and mission degradation lies in the interface between and the chemical/biological protective ensemble and the balance of mission equipment. The chemical/biological protective ensemble must integrate with ballistic protection, optics, and communication. The interface of the protective mask with the helmet accounts for a number of issues. Problems include disrupting the helmet suspension system, potentially compromising the seal of the mask, and the creation of irritating “hot spots.” Early integration between these systems must occur during concept refinement and technology development. An integrated chemical/biological ensemble that is a component or accessory to an integrated warfighter system, like the Army’s Ground Soldier System, may be the desired outcome. Achieving low-burden necessitates the innovative application of new technologies. A number of new technologies offer considerable opportunities in achieving integrated low-burden protection within a broadening threat spectrum without compromising needed performance. The growing field of nanostructured materials provides an opportunity to move beyond traditional materials such as



6 activated carbon and zeolites. One of the most exciting areas is reticular chemistry, which is described as the “linking of molecular building blocks of synthetic and biological origin into predetermined structure using strong bonds” (UCLA Center for Reticular Chemistry, http://crc.chem.ucla.edu/). The most well known class of these materials is Metal Organic Frameworks (MOFs) which have already exhibited absorbency potentials that far exceed activated carbon, and are currently being manufactured in commercial quantities. These compounds can be tailored to target specific classes of chemicals that include performance-limiting, high-volatility TICs. MOFs and similar compounds could be used to design smaller and lower-profile filter beds that protect against the expanding spectrum of threats. Smaller and lower profile filters decrease weight and reduce interference of the respirator with other mission systems. Reticular chemistry has the potential to go further. Reticular structures could be designed to contain an internal catalyst that detoxified the agent, or structures could be designed to adsorb as well as detect the compound or agent adsorbed. Another promising area has been the development of manufacturing techniques for nanofibers. These fibers have diameters on the scale of the meanfree-path of an air molecule. When nanofibers are used as a filter media the aerodynamics are governed by the “slip flow” or Knudsen regime with much lower drag than conventional flows. This implies that it may be possible to produce particulate filters with order-of-magnitude lower pressure drops, and high efficiency particulate filtration capabilities built into the clothing. In recent years, a number of innovations have just about made the production of these materials commercially viable. Additional developing technologies will make it possible to assemble these fibers into nano-composites that will include built-in adsorption, reactive, anti-microbial and sensing capabilities into a thin coating. This could revolutionize protective clothing and produce unconventional and extremely low burden approaches to respiratory protection. Incorporation of novel materials may allow the reinvention of collective protection systems. Novel, low-cost and scalable approaches that allow seamless incorporation into all building and vehicle designs and support rapid (field) conversion of fixed facilities are being sought. Novel system approaches may allow less dependence on overpressure techniques and rely more heavily on network integration and rapid response. Technologies that include strippable coatings, self-detoxifying surfaces and responsive (switchable) surfaces could support such novel configurations that address protection against external, as well as internal fugitive sources of contamination. Perhaps, more importantly, intrinsic and universal collective protection may be more constrained by our thinking. A more flexible approach that identifies areas and points of specific vulnerability may be in order. Settling for less protection in lower threat areas can facilitate investments in lower-cost approaches. Lower costs allow for universal design of protection. This will enable a sufficient degree of protection to be always available and will likely reduce the overall risk.


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Conclusion


Solutions to the challenge of low-burden protection depend on discovery, development and implementation of novel technologies. Of particular concern are technical challenges and expense associated with the development of new materials. Only by leveraging other funded areas of research can success be achieved. This requires partnering with industry through Cooperative Research and Development Agreements (CRADA) and developing and making use of cooperative agreements with allied countries. Despite the difficulty and expense of developing new materials, the technical opportunities present today assure a good chance of success. The risks imposed by the evolving nature of the threat demand the effort.


Nanoscience and Nanotechnology for Chemical and Biological Defense

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